1. Field of the Invention
The present invention relates to an image sensing apparatus for sensing radiation waves such as x-rays which can transmit through an object.
2. Related Background Art
Conventional image reading systems use, as one-dimensional line sensors and two-dimensional line sensors, reduction optical type CCD sensors using CCDS, CMOS sensors having an amplifier for amplifying electric charges accumulated in photoelectric conversion elements, equal magnification optical type CIS sensors using amorphous silicon (a-Si) or the like.
One of various types of such image sensors is an image sensing apparatus commonly used for sensing x-ray photographs. One of such apparatuses is an equal magnitude type image sensing apparatus which obtains image signals with a photoelectric conversion apparatus for converting x-rays, transmitted through an object and then propagated through optical fibers arranged two-dimensionally in parallel, into electric signals.
This image sensing apparatus is called an x-ray image sensor and has an x-ray scintillator formed on a fiber optic plate and adhered to an image sensor. For example, such an x-ray device using a CCD sensor is presented in the document xe2x80x9cFIBER OPTIC PLATE WITH X-RAY SCINTILLATORxe2x80x9d published by Hamamatsu Photonics K. K.
With this x-ray image sensing apparatus, an x-ray scintillator converts an x-ray image of x-ray beams transmitted through an object into a visual ray image. Depending upon the material of the x-ray scintillator, about 30 to 70% of incident x-rays are absorbed, while some of the x-rays are not absorbed but instead are transmitted through the x-ray scintillator and become incident upon the sensor. X-rays incident upon the sensor may pass through the sensor substrate or be absorbed at the substrate potential. However, some of the x-rays incident upon the sensor are photoelectrically converted and are observed as bright points in an output image. In order to reduce such bright points, an x-ray image sensing apparatus which can absorb 90% or more of transmitted x-rays in an x-ray shield fiber optic plate has been proposed.
However, it is difficult to perfectly eliminate transmitted x-rays, and x-ray noise is generated at some occurrence frequency. This x-ray noise poses the following problems. An image sensing apparatus having optical black pixel areas is associated with a problem of a change in black levels of an image. This will be clarified with reference to FIG. 1.
A signal contains a dark signal in an optical black pixel area and an object image signal in a photoelectric conversion area. The optical black pixel area is covered with an A1 layer or the like to shield visual light from the sensor. An x-ray transmits through the A1 layer. Therefore, in optical black pixels into which x-rays enter, the level of the black pixel signal is not a black (i.e., dark) level but instead becomes noise, having a level higher than the black level, as shown in FIG. 1. Generally in an image sensing apparatus, this optical black level is clamped to set a black reference for an image signal. With such noise, the black level is clamped to a level on the brighter side. Therefore, in a horizontal line having optical black pixels into which x-rays enter, a horizontal strip noise appears in the image so that the image quality is degraded greatly.
If x-rays enter a peripheral circuit (such as a driver circuit or an output amplifier circuit) near the photoelectric conversion area, the image sensing apparatus may cause an erroneous operation. For example, a reset circuit in the drive circuit may generate noise which may temporarily stop the scanning operation or may shift the timing of a shift pulse. Other peripheral circuits may also generate noise due to the X-ray.
It is an object of the invention to improve the image quality by reducing image noise caused by radiation waves such as x-rays.
In order to achieve the above-described object, according to one aspect of the present invention, there is provided an image sensing apparatus comprising a converting member for converting a radiation wave into visual light, an image sensing area having a plurality of pixels for converting visual light converted by the converting member into an electric signal, and shielding means mounted in a partial area of the image sensing apparatus for shielding the radiation wave.
According to another aspect of the present invention, there is provided an image sensing apparatus comprising a conversion member for converting a radiation wave into visual light, an image sensing area having a plurality of pixels for converting visual light converted by the converting member into an electric signal, a selector circuit for selectively reading signals from the plurality of pixels in the image sensing area, and a shielding member mounted above the selector circuit for shielding the radiation wave.
According to still another aspect of the present invention, there is provided an image sensing system comprising an image sensing apparatus including a conversion member for converting a radiation wave into visual light, an image sensing area having a plurality of pixels for converting visual light converted by the conversion member into an electric signal, a shielding member mounted in a partial area of the image sensing apparatus for shielding the radiation wave, and a selector circuit formed under the shielding member for selectively reading signals from the plurality of pixels in the image sensing area. An image signal processing circuit is provided for processing signals from the image sensing apparatus and a radiation wave generator is provided for radiating the radiation wave toward the conversion unit.